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Recipient filtering methods compared

ETRN makes available several different recipient filtering options. These include:

Recipient filtering methods compared
Filtering Method Description What is a "user"? Advantages Limitations
No recipient filtering In this configuration ETRN accepts e-mail for any e-mail address in the customer's domain(s). There are no controls in place to reject invalid recipients. Each unique e-mail address counts as a user.
  • Easy - no setup required
  • No cost controls. There is no limit to the number of users that you may be billed for.
  • The customer's server must be configured to accept any e-mail address in the customer's domains (must not reject invalid recipients).
  • Mailguard cannot be configured to automatically create new user accounts. Individual user accounts must be created manually.
  • If ETRN is providing outgoing SMTP relay, bounce e-mails (e-mails with a null sender) will not accepted. This may include e-mails like "Out of Office" auto-replies. This is done to prevent ETRN from being labeled as a backscatter spam source.
SMTP based recipient filtering In this configuration the ETRN system will query the customer's server before accepting e-mail for a new e-mail address. This data is cached to limit the number look-up required and to enable the system to accept e-mail when the customer's system is unavailable. Each unique e-mail address counts as a user.
  • Helps to control costs. The customer is not charged for e-mail sent to invalid e-mail addresses.
  • Works automatically.
  • Enables more Mailguard features.
  • Enables ETRN to accept bounce e-mails from the customer.
  • Higher costs. Each unique e-mail address counts as a user.
  • The customer's server must be configured to reject e-mail for invalid e-mail addresses.
  • Because of caching, the system may consider a newly created e-mail account to be invalid for several hours if a sender attempted to reach the new address prior to it being created in the customer's system.
  • Does not work well in combination with E-Mail Spooling in a Backup MX configuration.
Recipient White-list based recipient filtering In this configuration the customer utilizes the Recipient White-list feature of the Queue Management System to define the valid e-mail addresses in their domain. Each unique e-mail address counts as a user.
  • Helps to control costs. The customer is not charged for e-mail sent to invalid e-mail addresses.
  • Enables more Mailguard features.
  • Enables ETRN to accept bounce e-mails from the customer.
  • Higher costs. Each unique e-mail address counts as a user.
  • The customer must keep the Recipient White-list up to to date.
  • Incomplete support for multiple domains under a single account.
HTTP based recipient filtering In this configuration the ETRN system retrieves a list of valid e-mail addresses from a remote host, typically via HTTP. The customer defines their own logic for creating and maintaining this data. Each unique e-mail address counts as a user.
  • Helps to control costs. The customer is not charged for e-mail sent to invalid e-mail addresses.
  • Works automatically
  • Enables more Mailguard features.
  • Enables ETRN to accept bounce e-mails from the customer.
  • Higher costs. Each unique e-mail address counts as a user.
LDAP based recipient filtering In this configuration the ETRN system retrieves a list of valid e-mail addresses from the customer's system via LDAP. The LDAP Query can be customized to better suite the customer's specific needs. This configuration typically yields the best value to the customer. A user is defined as an Exchange mailbox for Exchange environments.
  • Best cost controls. The customer is billed only for their Exchange mailboxes. Aliases and other objects are free.
  • No charge for multiple domains.
  • Works automatically
  • Enables more Mailguard features.
  • Enables ETRN to accept bounce e-mails from the customer.
  • The ETRN system needs LDAP access to the customer's system.
MailGuard based recipient filtering In this configuration the ETRN system retrieves a list of valid e-mail addresses from our MailGuard system. A user is defined as a MailGuard user.
  • Good cost controls. The customer is billed only for the MailGuard users they have configured. Aliases are free.
  • Supports complex multi-domain alias configurations.
  • Enables ETRN to accept bounce e-mails from the customer.
  • The customer must keep their Mailguard users up to date.
  • MailGuard must be configured so that users are not created automatically.
DR based recipient filtering In this configuration the ETRN system retrieves a list of valid e-mail addresses from the customer's DR account. This configuration typically yields a user count very near to their in-house systems. A user is defined as a DR mailbox.
  • Good cost controls. The customer is billed only for their DR mailboxes. Aliases are free.
  • Works automatically with the DR system
  • Enables more Mailguard features.
  • Enables ETRN to accept bounce e-mails from the customer.
  • For accurate recipient filtering the customer must match the accounts in their DR environment to their in-house systems.
  • A catch-all account cannot be configured in the DR environment.

If the above recipient filtering methods don't fit your specific needs, please contact us. We can probably develop a custom solution for you.

We Answer Your Questions: FAQ

Q: What is the maximum e-mail attachment size?

A: The ETRN.com e-mail servers do not limit the size of individual e-mail attachments. The ETRN.com e-mail servers do impose a 400 MB maximum total message size limit. Individual customers can choose a smaller message size limit. We can also customize the handling of "over-sized" e-mails. Please contact us to discuss your specific needs. A couple of important facts:

1. Attachments are typically encoded in what is called Base64[1]. As a result, the actual length of MIME-compliant Base64-encoded binary data is usually about 137% of the original file size.

2. E-mails often contain both plain text and HTML components. This also increases the overall size of the e-mail.